A quantitative computer-assisted analysis of disc displacement in patients with internal derangement using sagittal view magnetic resonance imaging.

Forty patients diagnosed clinically as having internal derangement of one or both temporomandibular joints underwent magnetic resonance imaging. Seventy-three films were obtained: 26 films from 13 patients with bilateral symptoms; 40 films from 20 patients with unilateral symptomatic joints; and seven films from only the symptomatic joint in the remaining seven patients. Disc positions were evaluated in all of these films, and also in 17 films obtained from 10 asymptomatic volunteers. A system for quantitative measurement of disc position relative to the condyle in the closed-mouth position was used in two ways: manually, with an operator locating reference points and measuring them; and computer-assisted, with a special program developed to locate and measure these points. There was no significant difference in the results produced by these two methods. Important findings of this study were as follows: 1) 35% of the joints in the asymptomatic volunteers were found to have moderately or severely displaced discs; 2) only 75% of the joints diagnosed clinically as having an internal derangement were found to have significant disc displacement, which suggests that the other 25% must have had a different pathologic basis for the symptoms; and 3) the contralateral disc in the unilateral patients was found to be displaced as often as the disc on the symptomatic side (75%).